The present invention relates to video, voice, and data communications. More particularly, the present invention relates to increasing the speed and efficiency of upstream communications between a data service hub and a subscriber optical interface.
The increasing reliance on communication networks to transmit more complex data, such as voice and video traffic, is causing a very high demand for bandwidth. To resolve this demand for bandwidth, communication networks are relying more upon optical fibers to transmit this complex data. Conventional communication architectures that employ coaxial cables are slowly being replaced with communication networks that comprise only fiber optic cables. One advantage that optical fibers have over coaxial cables is that a much greater amount of information can be carried on an optical fiber.
This need for increased data transfer rates is fueled by the various types of applications being supported by both optical network architectures and the computers that are connected to them. Applications requiring increased bandwidth and data transfer rates include scientific modeling, engineering, publications, medical data transfer, data warehousing, network back-up applications, desktop video conferencing, and interactive whiteboarding.
Many of these applications require the transmission of large files over a network. File sizes can include hundreds of megabytes to gigabytes. Scientific applications demand ultra-high bandwidth networks to communicate three dimensional visualizations of complex objects ranging from chemical structures to engineering drawings. Magazines, brochures and other complex, full-color publications prepared on desktop computers employ optical networks to transmit data directly to digital-input printing facilities.
Many medical facilities are transmitting complex images over local area networks and wide area networks, enabling the sharing of expensive equipment in specialized medical expertise. Engineers are using electronic and mechanical design automation tools to work interactively and distributed development teams, sharing files in the hundreds of gigabytes. Data warehouses may comprise gigabytes or terabytes of data distributed over hundreds of platforms and accessed by thousands of users, and must be updated regularly to provide users near-real time data for critical business reports and analysis.
To address the enormous bandwidth concerns of the aforementioned applications, point to multipoint optical networks architectures have been contemplated. With such optical network architectures, data transfer upstream from the multipoints to the point often requires the use of predetermined timing schemes, such as time division multiple access (TDMA).
Under the predetermined timing scheme of TDMA, multiple data sources must start and stop transmitting data rather quickly during a predefined interval. With conventional optical transmitters, a certain amount of time within any TDMA scheme must be allocated to allow an optical transmitter to power up to an operating level for data transmission and then to power down at the end of a data transmission. Further, additional time must be allocated in any TDMA scheme for allowing an optical receiver to adjust itself when receiving different signals from optical transmitters that may have different properties (such as signal strength, noise, and other factors).
This allocation of transition times within any TDMA timing scheme decreases efficiency of data transfer, due to reduction of the rate at which data is transferred from multipoints to a single point in an upstream direction. The aforementioned problems are linked to the hardware supporting the optical communications. This hardware is needed to support a very popular and conventional broadband networking standard referred to as the synchronous optical network (SONET). A standard similar to SONET is referred to as the synchronous digital hierarchy (SDH) outside of the United States.
The majority of optical transmitters and receivers are designed to propagate data that is formatted according to the SONET transmission standard. One of the problems associated with the SONET transmission standard that accentuates or magnifies the limitations of current conventional optical transmitters and receivers is that the minimum frequency content of data formatted according to the SONET standard can extend to very close to zero by virtue of the SONET standard permitting the transmission of up to 72 or more bits of the same type (the 1 or 0).
In other words, the SONET transmission standard could potentially format data such that a string of 72 or more bits could be propagated that does not have a change in state. Such a transmission state of identical or similar bits requires the optical transmitters and the optical receivers to be designed at very low frequencies compared to or relative to other network protocols.
Another problem and drawback of conventional optical transmitters and optical receivers is that such equipment can have costs that approach (at the time of the writing of this text) of upward of hundreds of thousands of dollars. Accordingly, in light of the problems identified above with respect to conventional network protocols and conventional optical equipment, there is a need in the art for a method and system for efficient propagation of data and broadcast signals over an optical network. There is a need in the art for a method and system that can increase the speed in which optical transmitters and optical receivers can handle data in an upstream direction relative to a subscriber and a data service hub. Specifically, a need exists in the art for a method and system that can increase the speed at which data is transmitted from multiple points to a single point, by reducing wasted time spent switching transmission from one point to another.
A further need exists in the art for optical receivers that have increased speed to switch from receiving signals from one optical transmitter to another optical transmitter. And lastly, there is a need in the art to provide optical network equipment that can support an optical network protocol at a substantially reduced cost compared to the equipment needed to operate conventional network protocols such as SONET.
The present invention is generally drawn to a system and method for efficient propagation of data and broadcast signals over an optical network. More specifically, the present invention is generally drawn to a method and system that increases the speed in which optical transmitters and optical receivers can handle data in an upstream direction relative to a subscriber and a data service hub.
According to one exemplary aspect of the present invention, an optical network architecture can include a laser transceiver node and a subscriber optical interface. The laser transceiver node can comprise an optical receiver that can convert upstream optical signals received from the subscriber optical interface into upstream electrical signals destined for a data service hub. Meanwhile, the subscriber optical interface can comprise an optical transmitter such as a laser operating according to a predetermined timing scheme that produces the upstream optical signals received by the optical receiver housed in the laser transceiver node.
Both the optical transmitter of the subscriber optical interface and the optical receiver of the laser transceiver node can handle a frequency of data that is formatted according to a predetermined network protocol that is encoded with a predetermined coding scheme, and that is transmitted according to a predetermined data transmit timing scheme.
A frequency of the data transmitted according to the predetermined protocol can comprise an occupied frequency of a protocol that is defined as the lowest frequency of a frequency spectrum when the data comprises a maximum number of like bits permitted by the predetermined network protocol. The optical transmitter and optical receiver can have time constants that are adjusted according to this lowest occupied frequency of data when data is formatted according to the predetermined network protocol that can comprise Gigabit Ethernet (part of the IEEE 802.3 standard), that is encoded with 8B/10B encoding, and that is propagated upstream according to time division multiple access (TDMA).
In other words, the high frequency circuits present in the optical transmitter and optical receiver can have time constants that can be adjusted for maximum efficiency when supporting data formatted according to the predetermined network protocol comprising Gigabit Ethernet with 8B/10B encoding and that is transmitted according to TDMA.
Similarly, the time constant of a power level circuit of each optical transmitter can be adjusted to increase the speed to power up a laser that generates the optical signals corresponding to the data. Other high frequency circuits of each optical receiver can have time constants that are adjusted to maximize efficiency for receiving the predetermined network protocol comprising Gigabit Ethernet with 8B/10B encoding according to a predetermined timing scheme. Other high frequency circuits can include, but are not limited to, an optical detector circuit, an optional automatic gain control circuit, and a limiting/conversion circuit.
Specifically, the optical receiver of the laser transceiver node can be optimized for maximum efficiency when handling upstream data formatted according to Gigabit Ethernet with 8B/10B encoding and a predetermined timing scheme such as TDMA. When the optical receiver""s high frequency circuits have time constants that are adjusted to a specific frequency or range of frequencies, the device can rapidly switch from receiving signals from one optical transmitter to another. In other words, the optical receiver can make necessary adjustments such as gain control more quickly when receiving optical signals from different optical transmitters.
The quality of received optical signals generated by each optical transmitter can vary because of the different relative distances the optical signals are transmitted over an optical network. Other factors that can cause optical signals generated by one transmitter to be different from another transmitter can include laser power variation, optical component loss variation, and other similar factors known in the art. Further, an optical transmitter usually does not transmit readable data when the transmitter first starts transmitting. The optical receiver usually needs to make adjustments to compensate for the differences in the optical signals in order to accurately convert the optical signals into the electrical domain.
For each high frequency circuit mentioned above, adjusting of the time constant can comprise adjusting capacitance values to correspond to the frequency of data propagated according to the predetermined network protocol comprising Gigabit Ethernet with 8B/10B encoding and a predetermined timing scheme such as TDMA, according to one exemplary embodiment. This usually means that the high pass time constants of each high frequency circuit can be set lower than time constants designed to handle data formatted according to different conventional protocols such as SONET.
The lower time constants achieved according to the present invention generally correspond with data formatted according to a predetermined network protocol comprising Gigabit Ethernet with 8B/10B encoding and TDMA. However, other network protocols, encoding, and data transmit timing schemes for propagating data are not beyond the scope of the present invention. For example, other network protocols can include, but are not limited to, Fiber Distributed Data Interface (FDDI) and Digital Video Broadcasting-Asynchronous Serial Interface (DVB-ASI). Other encoding schemes can include, but are not limited to, 16B/18B and 64B/66B encoding. Meanwhile, other data transmit timing schemes can include, but are not limited to, time division multiplexing (TDM) or code division multiple access (CDMA).
By adjusting the time constants mentioned above, the present invention can increase the operating speeds for both the optical transmitter housed in the subscriber optical interface and the optical receiver housed in the laser transceiver node. Specifically, when the time constants of the optical transmitter are adjusted, data transmission can be increased since the delays normally attributed to start-up and power down times for the optical transmitter can be significantly reduced. This start up and power down time reduction for an optical transmitter can substantially improve data transmission rates when optical transmitters share bandwidth according to data transmit timing schemes such as time division multiple access (TDMA).